package r21310.chap06.d1204;

import javax.swing.*;

public class Demo01 {
    public static void main(String[] args) {
        String r= JOptionPane.showInputDialog("请输入圆的半径");
        Integer rr=Integer.valueOf(r);
        double area=Math.PI*rr*rr;
        System.out.println(area);
    }
}
